In California, there is the Caldor Fire raging right now in South Lake Tahoe. Heres what it looks like on the ground: https://www.reddit.com/r/weather/comments/pfczpl/caldor_fire...

The highest purple air sensor, near/on the fire front, in raw PM2.5 ug/m³ is at 368 when I checked: https://www.purpleair.com/map?opt=1/mPM25/a10/cC0&select=735...

Well, if you find it hard to believe, I welcome you to visit us and live here for a year or two. Don't forget to bring a good supply of spare lungs.

These measurements are supported by the official (state-sponsored) air quality monitoring.

I am not saying we have 1000+ micrograms 24/7. The daily average in winter time is closer to 300-500, depending on your location. However, I see such extreme measurements pretty much every single evening, with some going above 1500 µg/m³.

Back in the days of the great London smog particulate concentrations were going up to 5 _milli_grams per cubic meter:

https://sci-hub.se/https://pubmed.ncbi.nlm.nih.gov/29596258/...

It's not impossible or even particularly unusual.

I don't think the purple air sensors (laser scattering plantower sensors) are very accurate at such extreme measurements. There are numerous laboratory permanent sensors deployed by various state, federal and local authorities that you can compare. I've seen purple air at much more extreme values. Still terrible.

I expect there are a lot of particles bigger than 2.5 um?

I think you have us all curious now - where do you live? Sounds like Siberia, except I'd expect there to be more wind.

Relatively close, but no cigar. I'll quickly deanon myself if I describe the exact place, there's not many HNers here.